* Astronomy

The multiverse: a theory in trouble

How do you know they're black holes? - Physicist Lawrence Krauss, after being told that the universe is full of black holes.



It appears that those cosmic gluttons called black holes may be a figment of physicists imagination.
For years it has been thought that Einsteins theory of gravity (general relativity) required a fatal attraction around super-massive objects, causing the creation of black holesdreadful objects where nothing, not even light, can escape their greedy grasp. The idea that physics predicts stellar objects that gobble up everything in their gravitational web has spawned a spate of sci-fi speculations about spacetime rips, time-tunneling, and multiple universes.

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A Technion-Israel Institute of Technology physicist has developed a theoretical model of a time machine that could enable future generations to travel into the past. In his paper published in the July issue of Physical Review, noted time-travel theorist Professor Amos Ori provides practical solutions to a number of criteria long seen by other experts as obstacles to the realisation of time travel.
Ori's theory is actually a set of mathematical equations describing hypothetical conditions that, if established, could lead to the formation of a time machine, technically known as "closed time-like curves."

Previous theories addressing time travel are well grounded in Einstein's General Relativity theory. Renowned physicist Stephen Hawking has called time travel "an important subject for research," but has also proposed some of the strongest challenges to the concept. General Relativity states, among other things, that the gravitational pull of large objects such as planets can actually bend time and space. Time travel research is based on bending space-time so far that the time lines actually bend back on themselves to form a loop.

"We know that bending does happen all the time, but we want the bending to be strong enough and to take a special form where the lines of time make closed loops. We are trying to find out if it is possible to manipulate space-time to develop in such a way" - Amos Ori.

While the possibility of time travel has never been eliminated, scientists have identified a number of physical challenges, including the perceived need for some form of exotic matter with negative density. Such matter is predicted by quantum field theory to exist, though only in quantities too small for the construction of a time machine.
In a 2004 paper, Ori outlined a set of conditions that would allow for the creation of a time loop without the need for exotic matter. That theory called for the time loop to form as a donut-shaped vacuum, inside which time would curve back on itself, so that a person travelling around the loop might be able to go further back in time with each lap. A sphere containing non-exotic, but unidentified matter, would in turn envelop the loop.
Ori's latest work eliminates the need for that unidentified matter. His new calculations show that the envelope can in fact be filled with dust, a simple modelling of which is used regularly in theoretical physics, while still allowing for the evolution of a time machine.
Ori also addresses the possibility of the initial conditions forming a point of infinite gravitational field that no one could pass (instead of a time travel loop). His current paper outlines a more robust system that would prevent such an occurrence.

"The internal core is now mathematically protected, and it is easy to show that no irregularity could penetrate it" - Amos Ori.

The paper also more thoroughly defines the required spherical envelope.
Ori says serious questions remain about the overall stability of a time machine. His own calculations - done in collaboration with Technion Ph.D. student Dana Levanony - and those of other physicists, suggest that the evolution of a time machine would be dependent on a very narrow range of initial conditions that might be difficult - or even impossible - to achieve. He is also working to show ways such a configuration could be achieved.

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Title: Did time begin? Will time end?
Authors: Paul H. Frampton
(version v2)

Did time begin at a Big Bang? Will the present expansion of the universe last for a finite or infinite time? These questions sound philosophical but are becoming, now in the twenty-first century, central to the scientific study of cosmology. The answers, which should become clarified in the next decade or two, could have profound implications for how we see our own role in the universe. Since the original publication of Stephen Hawking's  A Brief History of Time in 1988, the answers to these questions have progressed as a result of research by the community of active theoretical physicists including myself. To present the underlying ideas requires discussion of a wide range of topics in cosmology, especially the make up of the energy content of the universe. A brief summary of my conclusions, that of three different possibilities concerning the history and future of time, the least likely is the conventional wisdom (time began and will never end) and most likely is a cyclic model (time never begins or ends), is in the short final Chapter which could be read first. To understand the reasoning leading to my conclusions could encourage reading of my entire book. My hope in writing this, my first popular book, is that it will engender reflection about time. Many a non-scientist may already hold a philosophical opinion about whether time begins and ends. This book's aim is to present some recently discovered scientific facts which can focus the reader's consideration of the two short questions in my title.

Read more (75kb, PDF)

Title: Did time begin? Will time end?
Authors: Paul H. Frampton

Did time begin at a Big Bang? Will the present expansion of the universe last for a finite or infinite time? These questions sound philosophical but are becoming, now in the twenty-first century, central to the scientific study of cosmology. The answers, which should become clarified in the next decade or two, could have profound implications for how we see our own role in the universe. Since the original publication of Stephen Hawking's  A Brief History of Time in 1988, the answers to these questions have progressed as a result of research by the community of active theoretical physicists including myself. To present the underlying ideas requires discussion of a wide range of topics in cosmology, especially the make up of the energy content of the universe. A brief summary of my conclusions, that of three different possibilities concerning the history and future of time, the least likely is the conventional wisdom (time began and will never end) and most likely is a cyclic model (time never begins or ends), is in the short final Chapter which could be read first. To understand the reasoning leading to my conclusions, which go against the views in other books on cosmology but which I think are likely to prevail, could encourage reading of this entire book. My hope in writing this, my first popular book, is that it will engender reflection about time. Many a non-scientist may already hold a philosophical opinion about whether time begins and ends. This book's aim is to present some recently discovered scientific facts which merit the reader's consideration.

Read more (75kb, PDF)